Synthetic polymers have been developed and used as flocculating agents in processes for the recovery of natural resources. For such processes, there is an increasing demand for polymers which will withstand hostile environments including, e.g. high temperatures, high salinity, and high content of multivalent metal cations, commonly known as "hardness ions", as well as the high acidity, temperature and shear conditions which are often encountered.
In processing mineral ores, it is often necessary to separate finely divided solids from aqueous suspension; conversely, in treating water for use, e.g., for municipal water supplies or industrial applications, it is often necessary to remove finely divided solids which may be suspended therein. Improvements in the ease of separation of finely divided solids from aqueous suspension either by sedimentation or by filtration have been accomplished by incorporating small amounts of high molecular weight water-soluble polymers in such suspensions. Among such polymers which have proven to be effective on a wide variety of ore suspensions are high molecular weight polyacrylamide polymers and the hydrolysis products thereof. Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 10, p. 489-548 (3rd Ed-1980), whose teachings are herein incorporated by reference, teaches the use of cationic, anionic and nonionic polymers as "Floculating Agents" and in "Flotation". Improved polymers have also been developed for this purpose; for example, Sullivan discloses in U.S. Pat. No. 3,146,193 (1964) certain high molecular weight water-soluble copolymers of certain vinyl substituted, nitrogen-containing, heterocyclic ring compounds with acrylamide which can be incorporated in aqueous suspensions of finely divided inorganic solids to facilitate the concentration and separation of such solids.
Processes using improved polymers are in demand for the treatment of concentrated brine solutions, e.g., potash ore processing. As an example, the American potash industry annually treats more than 18 MM tons of ore from which more than 3 MM tons of potash concentrate is recovered. Most of this product is used as fertilizer; however, nearly all of the potassium required by other U.S. industries comes from this concentrate.
A typical potash ore consists of sylvite (20-25%), halite (60-75%), and clay (4-20%). The potassium containing mineral is sylvite (KCl). The major impurities are halite (NaCl) and clay. The mixed ore is processed at the mine site. The processing varies with the level of clay, the higher clay ores requiring a more extensive treatment. This extensive treatment is becoming more widely utilized as the mines grow more mature and use lower grade ores.
The adverse effect of clay is caused by the high affinity of potash collectors for clay. The potash collectors are chemical compounds which ideally adsorb onto sylvite and then facilitate the flotation separation process. The affinity of the collector for clay diminishes the cost effectiveness of the overall process which typically consists of subsequent crushing, grinding, hydrolytic clay removal, and flotation steps. As a result, the time, cost and steps required are dependent upon the clay content. When more than a few percent of clay is present, the clay must be "blinded" by a polymer which historically has been polyacrylamide, guar gum, or potato starch before addition of the collector.
A preferred step would be clay removal by flocculation with a brine soluble polymer, since all processing is conducted in saturated brine to prevent mineral dissolution. This polymer, in addition to brine solubility, must retain its activity and thus cost effectiveness in the presence of the high ionic strength brine medium. The effectiveness of most polymers, such as the polyacrylamides, are reduced, and in many cases the polymers are actually precipitated in such brines. Thus, effective flocculating agents which will withstand such saturated brines are in demand.